As a solar cell backsheet material, fluorine resin films (e.g. polyvinyl fluoride (PVF) films) and polyethylene terephthalate (PET) films to which aluminum foil lamination, aluminum vapor deposition or Si vapor deposition is applied have been used in view of improvement in the weather resistance and gas barrier properties. Humidity-sensitive solar cells are protected from moisture by providing such a backsheet.
Among the backsheet materials described above, a fluorine resin film is superior from the viewpoint of its long-term durability. Therefore, a growing demand for such fluorine resin films as the backsheet material has risen. However, there are problems that adhesive properties of the material consisting of the fluorine resin having a C—F bond are generally poor because such material has a small surface energy, resulting in showing water- and oil-repellent properties.
The technology that improves the adhesive properties of such a fluorine resin film includes, for example, plasma discharge processing, corona discharge processing, flame processing, blast processing, and the like (cf., e.g., the following non-patent documents 1 to 4). These surface modification technologies have improved the adhesive properties by introducing a hydrophilic functional group (e.g., —COOH group, —OH group, SO3H group, SO2Fx group, etc.) into the resin surface.
However, the above processing method will require a large-scale apparatus, leading to an increase in production costs. In addition, there is also a problem that the adhesive properties cannot be maintained for a long period of time because of significant aging after the surface modification.